LITHOLOGICAL CORRELATION WITH TRACE ELEMENT ABUNDANCES AND MONAZITE STABILITY: IMPLICATIONS FOR FLUID AVAILABILITY IN THE METAMORPHIC AUREOLE OF THE BALLACHULISH IGNEOUS COMPLEX
Monazite abundances are variable and relatively low in the lowest grade rocks (0.00042-0.00118% Vol.), and, generally decrease to ≤0.00217% Vol. at ~600°C. In samples metamorphosed at >600°C, an increase in monazite abundances occurs in all all transects (≤0.013% Vol.). From regional grade through ~610°C in rocks of the Creran Succession transect collected foliation-parallel, monazite occurs as individual grains or inclusions. In equivalent rocks of the other transects, monazite occurs as elongate clusters and frequently in association with biotite. Monazite above 610°C in all transects shows no systematic variation in grain size or distribution.
Monazite occurrence and abundance correlate with temperatures through 600-620°C, but not necessarily with whole-rock major or rare earth element abundances. In the Creran Succession, the transect parallel to foliation shows increased monazite abundances with higher REE abundances. However, in the transect sub-perpendicular to foliation the pattern is non-systematic. This suggests that there is a second-order process or REE-mineral controlling the local distribution and abundance of monazite.